A hybrid vehicle which uses an engine and an electric motor as the motive source for a vehicle is known.
This type of hybrid vehicle uses the output of the electric motor when the running load is small and switches to the output of the engine from the electric motor when the load is large. The engine and the electric motor are connected by a clutch. When the clutch is connected and the switch is made from the electric motor to the engine, a shock is generated on switching if there is a difference between the two outputs. Thus driving performance and driver comfort are adversely affected.
For example, when a vehicle accelerates from a low speed, a clutch is connected for the purpose of switching from driving on the electric motor to driving on the engine. At this time, the output of the engine is made to correspond with that of the electric motor before the engagement of the clutch so that a shock will not be generated at the time of switching. Furthermore it is necessary to place the output of the electric motor to zero at the moment that the clutch is connected. Actually since there is a response delay, this kind of control is not possible and the generation of a shock can not be avoided. Furthermore if there is a difference in the rotation speed between the engine and electric motor at the moment the clutch is engaged, not only will a shock be generated, but also the clutch will undergo wear.